Copper seawater corrosion

Since the formation nature and breakdown of protective surface films depends on both material and environmental parameters such influences on erosion corrosion will be discussed together. Particular attention will be paid to the copper/seawater and carbon steel/water (steam) systems. 

Efird KD. Effects of fluid dynamics on the corrosion of copper-base alloys in seawater. Corrosion, 33, 1977 3-8. 

B. Todd. Materials selection for high reliability copper alloy sea water system. Copper Development Association, www.copper.org/application/marine/seawater corrosion.html. 

B. C. Syiett and D. D. Macdonald [1979] The Validity of Electrochemical Methods for Measuring Corrosion Rates of Copper-Nickel Alloys in Seawater, Corrosion 35, 505-508. 

Concentrations of copper in seawater can cause accelerated corrosion of metalUc components. In unpolluted seawater, the copper concentration is 0.2 ppb, which is typically not high enough to influence a metal s corrosion behavior. If, however, the copper concentration is increased above approximately 30 ppb, corrosion of aluminum alloys can occur. The copper concentration may be increased due to a number of factors including copper leaching from antifouling paints, pollutants containing copper, or nearby copper alloy corrosion. If the copper deposits onto aluminum... 

S] Syrett, B. C., The Mechanism of Accelerated Corrosion of Copper-Nickel Alloys in Sulfide-Polluted Seawater, Corrosion Science. Vol. 21, 1981, p. 187. 

Strength at high temperature Inconels, Hastelloys Seawater corrosion resistance Copper, nickel, titanium alloys Creep resistance Steels and nickel alloys... 

Bailey, G. L., Copper Nickel Iron Alloys Resistant to Seawater Corrosion. Journal of the Institute of Metals, 79 (1951). 

Silver reduces the oxygen evolution potential at the anode, which reduces the rate of corrosion and decreases lead contamination of the cathode. Lead—antimony—silver alloy anodes are used for the production of thin copper foil for use in electronics. Lead—silver (2 wt %), lead—silver (1 wt %)—tin (1 wt %), and lead—antimony (6 wt %)—silver (1—2 wt %) alloys ate used as anodes in cathodic protection of steel pipes and stmctures in fresh, brackish, or seawater. The lead dioxide layer is not only conductive, but also resists decomposition in chloride environments. Silver-free alloys rapidly become passivated and scale badly in seawater. Silver is also added to the positive grids of lead—acid batteries in small amounts (0.005—0.05 wt %) to reduce the rate of corrosion. 

Nickel—Copper. In the soHd state, nickel and copper form a continuous soHd solution. The nickel-rich, nickel—copper alloys are characterized by a good compromise of strength and ductihty and are resistant to corrosion and stress corrosion ia many environments, ia particular water and seawater, nonoxidizing acids, neutral and alkaline salts, and alkaUes. These alloys are weldable and are characterized by elevated and high temperature mechanical properties for certain appHcations. The copper content ia these alloys also easure improved thermal coaductivity for heat exchange. MONEL alloy 400 is a typical nickel-rich, nickel—copper alloy ia which the nickel content is ca 66 wt %. MONEL alloy K-500 is essentially alloy 400 with small additions of aluminum and titanium. Aging of alloy K-500 results in very fine y -precipitates and increased strength (see also Copper alloys). 

Vanadium is resistant to attack by hydrochloric or dilute sulfuric acid and to alkali solutions. It is also quite resistant to corrosion by seawater but is reactive toward nitric, hydrofluoric, or concentrated sulfuric acids. Galvanic corrosion tests mn in simulated seawater indicate that vanadium is anodic with respect to stainless steel and copper but cathodic to aluminum and magnesium. Vanadium exhibits corrosion resistance to Hquid metals, eg, bismuth and low oxygen sodium. 

Uses. Copper—nickel—iron alloys, UNS C 96200 (90 10 copper nickel) and UNS C 96400 (70 30 copper nickel), are used in corrosion-resistant marine (seawater) appHcations. UNS C 96400 is used for corrosion-resistant marine elbows, flanges, valves, and pumps. Leaded nickel—brass, UNS C 97300 (12% nickel-silver), is used for hardware fittings, valves, and statuary and ornamental castings. 

Cupronickels (10 to 30 percent Ni) have become very important as copper alloys. They have the highest corrosion resistance of all copper alloys and find apphcation as heat-exchanger tubing. Resistance to seawater is particularly outstanding. 

The attraction of rubbed amber and some other effects of electricity were known in ancient times. We know from finding nails in an old wreck that the Romans knew about contact corrosion combined with electric current flow. A skin of lead as a protection against boring worms covered the wooden planks of the ship and was nailed down with copper nails. Galvanic coupIe.s formed between the lead and the copper nails and the less noble lead sheets around the nails corroded in the seawater and fell off. The shipbuilders discovered a simple solution and covered the heads of the copper nails with lead as well. Galvanic current flow between the two metals was eliminated and corrosion was prevented (26). 

Nickel is usually alloyed with elements including copper, chromium, molybdenum and then for strengthening and to improve corrosion resistance for specific applications. Nickel-copper alloys (and copper-nickel alloys see Section 53.5.4) are widely used for handling water. Pumps and valve bodies for fresh water, seawater and mildly acidic alkaline conditions are made from cast Ni-30% Cu type alloys. The wrought material is used for shafts and stems. In seawater contaminated with sulfide, these alloys are subject to pitting and corrosion fatigue. Ammonia contamination creates corrosion problems as for commercially pure nickel. 

Briefly the important developments in copper alloys with respect to their erosion corrosion behaviour in seawater have been ... 

The corrosion rates of wrought iron and mild steel when immersed in seawater or buried in soil are not significantly different when the copper contents are similar. 

Cathodic protection applications in fresh water include use of ferrite-coated niobium , and the more usual platinum-coated niobium . Platinised niobium anodes have been used in seawater, underground and in deep wells " and niobium connectors have been used for joining current leads Excellent service has been reported in open-seawater, where anodic potentials of up to 120V are not deleterious, but crevice corrosion can occur at 20 to 40V due to local surface damage, impurities such as copper and iron, and under deposits or in mud ... 

Aluminum and silicon bronzes are very popular in the process industries because they combine good strength with corrosion resistance. Copper-beryllium alloys offer the greatest strength and excellent corrosion resistance in seawater and are resistant to stress-corrosion cracking in hydrogen sulfide. 

The most common use of nickel is as an alloy metal with iron and steel to make stainless steel, which contains from 5% to 15% nickel. The higher the percentage of nickel in stainless steel, the greater the steel s resistance to corrosion—particularly when exposed to seawater. Nickel is also alloyed with copper to make Monel metal, which was widely used before stainless steel became more economical and practical. It was used for many purposes as varied as household appliances and general manufacturing. Nickel is also used to electroplate other metals to provide a noncorrosive protective and attractive finish. 

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